Protection of magnesium and magnesium base alloys against corrosion



Patented May 30, 1950 UNITED STATES PATENT OFFICE PROTECTION OF MAGNESIUM AND MAGNE- SEUM BASE ALLOYS AGAINST CORROSION No Drawing. Application April 2, 1948, Serial No. 18,716. In Great Britain April 3, 1947 2 Claims. 1

This invention relates to the protection of magnesium and magnesium base alloys against corrosion by immersion of the metal in a solution which reacts with the metal and produces a protective film on it.

We have encountered difficulties in applying hitherto known processes to the treatment of magnesium alloys which contain a small percentage of zirconium in accordance with British Patent No. 511,137.

The main object of the present invention is to provide a process which whilst suitable for the treatment of various magnesium base alloys, is well adapted to the treatment of magnesium alloys containing zirconium.

According to the present invention the metal is treated in an aqueous solution containing chromic acid ions, magnesium sulphate, and manganous sulphate, the solution having a pH value between 3 and 6 (preferably 4 to 6.0) and being used at room temperature. The chromic acid ions are conveniently provided by potassium and/or sodium dichromate which may be used in the proportions of 50 to 150 grams (e. g. 100 grams) to one litre of water.

The magnesium sulphate may be used in the proportions of 30 to 70 (e. g. 50 grams) of to one litre of water. The manganese sulphate may be used in the proportions of 30 to 70 (e. g.

50 grams) of MnSOeAI-IzO to one litre of water.

Thus the solution may consist of Water litre 1 Sodium dichromate grams 100 MgSO4.7H2O do 50 Mnso4.4HzO "do--- 50 A treatment of about two hours at room temperature produces an even black film on magnesium base alloys containing zirconium, with or without zinc, cadmium, or beryllium, and the solution also produces an effective film on magnesium, and on magnesium containing various proportions of aluminum with or without other alloying constituents.

The process can be carried out at room temperatures or with the solution maintained hot, e. g. boiling or at any temperature below boiling point. In other words the solution can be used either cold or hot according to th requirements of the user. If the solution is used at the boiling point the period of immersion may be reduced to about 10 minutes; the use of the solution hot results in satisfactory film formation, whilst retaining reasonably long life of the solution.

We claim:

1. A method of treating magnesium base a1- loys containing zirconium to afiord protection against corrosion, wherein the metal is reacted upon and a surface film is formed, which comprises immersing said metal in an aqueous solution which consists essentially of water, chromic acid ions, magnesium sulphate, and manganous sulphate, the solution having a pH value between 3 and 6, the manganese sulphate being present in a proportion of between 30 and grams of MnSO4A H2O to one litre of water, and the magnesium sulphate being present in quantity from 30 to 70 grams of MgSO4.7I-I2O- per litre of Water.

2. A method of treating magnesium base alloys containing zirconium to afford protection against corrosion, wherein the metal is reacted upon and a surface film is formed, which comprises immersing said metal in an aqueous solution which consists essentially of water as solvent and the following solutes: viz., at least one substance selected from the group consisting of the dichromates of potassium and sodium in the proportions of 50 to grams to one litre of water, and magnesium sulphate and manganous sulphate, each in the proportion of 30 to 70 grams of MgSO4.7I-I2O and MnSOulHzO respectively per litre of water, the solution having a pH value between 3 and 6.

SIMON E. MAYER. W. F. HIGGINS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,747,776 Jirotka Feb. 18, 1930 2,224,528 Sutton et al Dec. 10, 1940 2,288,552 Siebel et a1 June 30, 1942 2.352.076 Bushrod June 20, 1944 

2. A METHOD OF TREATING MAGNESIUM BASE ALLOYS CONTAINING ZIRCONIUM TO AFFORD PROTECTION AGAINST CORROSION, WHEREIN THE METAL IS REACTED UPON AND A SURFACE FILM IS FORMED, WHICH COMPRISES IMMERSING SAID METAL IN AN AQUEOUS SOLUTION WHICH CONSISTS ESSENTIALLY OF WATER AS SOLVENT AND THE FOLLOWING SOLUTES: VIZT, AT LEAST ONE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF THE DICHROMATES OF POTASSIUM AND SODIUM IN THE PROPORTIONS OF 50 TO 150 GRAMS TO ONE LITRE OF WATER, AND MAGNESIUM SULPHATE AND MANGANOUS SULPHATE, EACH IN THE PORTION OF 30 TO 70 GRAMS OF MGSO4.7HO AND MNSO4.4H2OP RESPECTIVELY PER LITRE OF WATER, THE SOLUTION HAVING A PH VALUE BETWEEN 3 AND
 6. 